In a conventional injection blow molding (IBM) machine, a preform or parison is injection molded into a mold, around a core rod. The injection mold is opened and the core rod and the parison are transferred to a blow molding station. The parison is then blown into the shape of the final article inside the blow mold. The blow mold is opened and the blown article is advanced to a station where it is stripped off the core rod.
Prior injection and injection blow molding machines include horizontally split mold halves with mold closure pressure applied by vertically actuated mold clamps. These clamps require tremendous amounts of hydraulic pressure to hold the mold halves closed during injection of the molding material. This is due to the extremely high injection pressures developed upon parison formation. Such force requires a very stable structure to which the force from the mold halves is transferred, as well as extremely close tolerances on the mold halves to prevent torquing and deformation of the mold halves under such great pressure. Hydraulic pressurized equipment provides precise force control of mold clamp thrust.
Although the hydraulic equipment performs the clamping function effectively, the presence of hydraulic equipment makes conventional IBM equipment ill suited for use in a clean-room environment. Minute quantities of the hydraulic fluid may escape from the press clamping mechanism. The hydraulic fluid that escapes may capture dust, bacteria and molds that are present in the air. The bacteria and molds reproduce, contaminating the clean environment.
Another feature of prior art injection blow molding systems is the use of separate mechanisms for: (1) raising and lowering the top halves of the parison and blow molds, and (2) the clamping mechanism for resisting the injection pressure. In a typical IBM machine of the prior art, a counterbalancing force is applied to the offset the weight of the press, so that a relatively small force is required to raise or lower the press (much smaller than the clamping force needed during injection). Thus, separate mechanisms are used to provide: (1) the small raising and lowering force; and (2) the large clamping force.
Alternate methods and machinery for performing the press clamping functions are desired.